1. Field of the Invention
The present invention relates to a base station and radio resource allocation method which performs allocation of a new radio resource in order to establish a radio link with a mobile station in a mobile communications system.
2. Related Background Art
In a mobile communications system which adopts a CDMA (Code Division Multiple Access) method, when there has been a communications request from a mobile station, provided that a radio channel and hard resources (incoming/outgoing signal processing section allocated for each call) for communicating with the mobile station can be guaranteed, a base station judges whether or not the radio resource usage volume at the time of the communications request is less than an allocation threshold value (predetermined fixed value), and if this radio resource usage volume is less than the allocation threshold value, then it allocates a new radio resource and establishes a radio link with the mobile station.
However, since the base station requires a high transmission power when sending data to the mobile station, then the radio resource usage volume may vary even whilst the number of mobile stations to which communications have been established remains the same, and hence problems of the following kind may arise in the base station which allocates radio resources in the foregoing manner.
For example, even in a situation where communications with the mobile stations are actually congested, there are times when data transmission to a multiplicity of mobile stations declines temporarily and the radio resource usage volume is less than allocation threshold value, and if a communications request is received from a mobile station at such a time, then a radio resource will be allocated and as a result, the radio resource capacity will be overwhelmed.
On the other hand, even in a situation where communications are actually being conducted with relatively few mobile stations, there are times when data transmission to a multiplicity of mobile stations increases temporarily and the radio resource usage volume exceeds the allocation threshold value, and if a communications request is received from a mobile station at such a time, then a radio resource will not be allocated and hence it will not be possible to use the radio resources in an efficient manner.